IR spectroscopy measurements may be useful for a variety of purposes including aerospace, automotive and industrial applications, as well as biological and bio-medical applications. For example, infrared (IR) radiation is readily absorbed by materials in association with relative motions (vibrations) of atoms such as carbon, hydrogen, oxygen and nitrogen. As such, IR spectroscopy measurements may indicate a condition of a wide variety of organic as well as inorganic materials.
Frequently, it is desirable to maintain a polymer resin material in a known state of cure (e.g., a known degree of polymer cross-linking) including a relatively uncured state prior to use of the polymer resin material. For example, an initially uncured (unaged) polymer resin material may tend to lose desirable properties, such as adhesiveness and flexibility, the longer the polymer resin material is removed from a freezer and exposed to the environment (aged), including storage under controlled environmental conditions, such controlled lighting and temperature conditions. The loss of desirable properties is related to complex chemical reactions that take place in the polymer resin material over time including polymeric cross-linking chemical reactions.
For example, certain polymer composite structural materials, such as those used in aircraft, are pre-impregnated (prepreg) with relatively uncured polymer resin material, which must then be maintained in a controlled environment, such as a frozen environment, prior to use in the formation of a laminated composite material structural part. The controlled environment is necessary in order to maintain the relatively uncured state and associated adhesive properties of the prepreg material which are important in forming composite laminates to build the structural part.
One problem with quality control of initially relatively uncured polymer resin materials, such as adhesives, surfacing materials, and laminating materials, is that prior art methods of determining a degree of aging or curing of the polymer resin material, requires removing samples of the material, thus, destroying a portion of the sample, and performing ex-situ time consuming laboratory analysis, during which time, the polymer resin material will age further. The state of cure for pre-preg materials is currently measured with liquid chromatography (LC), which requires a solvent extraction of the pre-preg and the proper laboratory equipment to perform the LC analysis. Current specifications for allowable pre-preg aging are based on the liquid chromatography analysis method with a ratio of two chromatogram peaks.
Other infrared(IR) non-destructive methods in the prior art used to measure the properties of thin films includes using IR absorbance to determine the amount of a chromated conversion coating on a metallic substrate (U.S. Pat. No. 6,794,631), determining the amount of an anodize coating on a metallic substrate, (U.S. Pat. No. 6,784,431), determining an amount of chemical cure and amount of surface contamination with filter infrared spectroscopy (U.S. Pat. No. 6,906,327), determining the amount/thickness of an opaque coating on a substrate (U.S. Pat. No. 6,903,339) and (U.S. Pat. No. 7,223,977), and determining an amount of heat damage to a resin-fiber composite substrate (U.S. Pat. No. 7,115,869), all of which are fully incorporated by reference herein.
None of the above methods and associated devices, however, disclose a method or device that is suitable for performing in-situ, real time IR spectroscopy including determining a degree of chemical curing (aging) of a polymer resin material, particularly where a portable, real-time capability is desirable, such as in aircraft manufacturing, assembly, maintenance, and repair of aircraft.
Thus, there is a continuing need for improved IR non-destructive testing methods including a method that is suitable for performing IR spectroscopy to determine a degree of chemical curing (aging) of a polymer resin material, including a portable, real-time IR spectroscopic method, including advantageously useable in aircraft manufacturing, assembly, maintenance, and repair of aircraft.
Therefore it is an object of the invention to provide a method that is suitable for performing IR spectroscopy to determine a degree of chemical curing (aging) of a polymer resin material, including a portable, real-time IR spectroscopic method, including advantageously useable in aircraft manufacturing, assembly, maintenance, and repair of aircraft.